Slide rule

A slide rule is an ancient mechanical instrument used to perform mathematical calculations. It consists of a series of parallel lines on which are arranged movable cursors. Each cursor is marked with numbers or measurement scales.

The slide rule works on the principle of proportions and logarithmic scales. With this tool, you can perform mathematical operations such as multiplication, division, square root, and so on, by sliding the sliders along the lines and reading the results on the scales.

Slide rules were popular before the advent of calculators and computers, and played an important role in engineering, navigation, science, and other areas requiring complex calculations. Although they have now been largely replaced by digital technology, slide rules are still prized for their elegance and historical value.

The ruler consists of three parts:

• a body on which there are fixed stairs
• a sliding pole with escalators, some in front, some in back
• a cursor with one or more reference lines

Stairs
Rules have different scales, depending on the type. Some are present on all rules, others only on those intended for particular operations. Scales are usually recognizable by a letter written on the left. The main ones are:

A: fixed scale of the squares on the fixed ruler;
B: escalator of squares on the slide;
C: sliding scale of numbers on the slide;
CI: inverse scale of numbers on the sliding, but sometimes on the fixed;
D: fixed number scale;
K: fixed cube scale;
L: fixed scale of decimal logarithms on the fixed;
S: sine scale, usually a movable scale on the slide, in Graphoplex slides on the back of the slide, sometimes a scale on the fixed;
ST: scale of sines and tangents for small angles, usually a scale on the slide, in Graphoplex rules on the back, sometimes a scale on the fixed one;
T: tangent scale, usually a sliding scale on the slide, in Graphoplex slide rules on the back, sometimes a scale on the fixed one;

Number scales do not indicate absolute values, but only the significant figures of scientific notation. It is up to the user to interpret each number by adding the correct order of magnitude.
In other words, the 1,2 mark on the number scale can also indicate numbers like 12 or 120, or numbers like 0,12 and 0,012.

Similarly, the decimal logarithm scale indicates only the fractional part of the logarithm, i.e. its mantissa, since its integer part corresponds to the order of magnitude of the number.

Anyone who wishes to contribute to improving this page can post their experience or memory in the comments section.